Manufacturers of disk drives often use magneto-resistive (“MR”) transducers (heads) instead of thin-film inductive (“TFI”) transducers to perform the disk drive's read functions because of the greater sensitivity of MR transducers over TFI transducers. Due to their sensitivity, however, MR transducers sometimes pickup spurious signals emitted by power transformers, motors and the like.
In an effort to reduce or eliminate the pickup of the aforementioned spurious signals and to flatten the frequency response of the readback signal, disk drive manufactures have placed shields around the MR transducers. Such shields, however, can negatively affect the performance of the MR transducer. Specifically, the shields have been found to be susceptible to variations in their magnetic states. These variations can be magnetically coupled to the MR transducer which can cause unwanted shield-related side readings. The data regions of the magnetic disk may not cause problematic variations in the magnetic state of the shield because the information placed on the disk is written in the data regions in a relatively random fashion. However, the servo regions of the disk have caused problematic magnetic variations in the shields and, hence, problematic shield-related side readings, because the servo-burst patterns are written in a radially coherent manner.
The above-described shield-related side readings may cause, among other things, a bias and/or bit shift in data that is written on a disk, and/or asymmetry and bit shift of a read signal when reading data from the disk, any of which may obscure the data bits. Shield-related side readings may also cause a decrease in the linear range of the MR transducer when reading off-track servo information and a decrease in the off-track signal-to-noise ratio. Furthermore, in extreme cases, the shield-related side readings can cause the disk drive to completely malfunction.